Estimate gravel, perforated pipe, filter fabric, excavation, weight, and optional cost for a simple French drain using dimensions supplied by your project design.
The trench is modeled as a rectangular prism. A custom gravel zone can include material below and above the pipe, and the pipe’s outside cylinder can be subtracted from gravel volume.
Project gravel waste and pipe extra are applied separately after included runs are summed.
The initial trench dimensions, pipe diameter, gravel depths, allowances, and optional slope are editable estimating inputs—not drainage-design recommendations.
excavation = length × width × trench depthgravel depth = below-pipe gravel + pipe outside diameter + above-pipe gravelpipe volume = π × (outside diameter ÷ 2)² × pipe lengthplanning gravel = (gross gravel zone − pipe displacement) × (1 + waste rate)bottom + sides = width + 2 × gravel depth; full wrap = 2 × width + 2 × gravel depth + overlapFor a 100 × 1 × 2 ft full-fill trench with a 4 in outside-diameter pipe, gross gravel-zone volume is 200 ft³. Subtracting about 8.727 ft³ of pipe leaves 191.273 ft³; a 10% gravel allowance produces about 210.401 ft³, or 7.793 yd³, of planning gravel.
With 6 in below, 4 in pipe, and 6 in above, the gravel zone is 16 in deep.
A 100 ft drain with 10% pipe extra requires 110 ft; 10 ft stock sections require 11 pieces.
A 1 ft trench with a 1.5 ft gravel zone requires 4 ft-wide fabric for bottom plus both sides.
Only the pipe’s external cylinder displaces gravel; internal pipe volume is not subtracted.
Gravel weight varies by material and moisture, so density is optional and user supplied.
Gravel waste, pipe extra, and fabric waste are editable project inputs applied independently once.
A fabric roll narrower than the calculated wrap width may require seams or another layout.
Custom vertical layout counts only the entered gravel envelope. Remaining trench depth is treated as unspecified backfill, not gravel. The entered layer depths and pipe size must come from the project design.
The fabric estimate models bottom and sides or a full wrap. Roll calculation uses drain length when roll width can cover the required cross-section; it does not select a filter product or determine soil compatibility.
Optional user-entered density converts planning volume to mass. Bag quantities use manufacturer volume yield; weight purchasing requires density.
Gross bank excavation and optional user-entered swell are estimates. An entered slope percentage produces elevation drop only and is not a drainage, hydraulic, or safety recommendation.
Authoritative drainage guidance treats aggregate, pipe, outlets, and filters as design components whose suitability depends on the system and site. This calculator only estimates quantities from entered geometry; it does not evaluate soil infiltration, groundwater, capacity, outlet adequacy, stormwater rules, or local requirements.
Calculate the entered gravel envelope, subtract optional outside-pipe displacement, then add the selected project waste.
Multiply drain length, trench width, and gravel-zone depth, then subtract pipe displacement where appropriate.
Base pipe length equals included drain lengths; add the selected pipe extra separately.
Yes when the outside of the pipe occupies the gravel envelope; the option can be disabled when it does not.
The calculator does not prescribe this; enter the depth required by your project design.
Enter the design depth and ensure the complete vertical gravel zone fits the trench.
Multiply the required cross-section wrap width by drain length and add fabric waste.
Bottom plus sides uses trench width plus twice gravel depth; a full wrap also includes the top and overlap.
The result converts the unrounded planning volume to cubic yards.
Weight requires an approximate supplier or material density.
Multiply trench length, width, and depth.
This calculator does not prescribe slope; it only computes drop from a slope entered by the user.
The calculator does not select pipe diameter or drainage capacity.
No. Hydraulic and site design require project-specific evaluation.